Semiconductor devices such as electronic devices like DRAMs and logic integrated circuits (an interconnect structure comprising such elements as an electrically conductive layer and conductors) formed on the wafer (substrate) have been protected by providing an electrically insulating layer on the circuit surface. In the case of semiconductor devices that employ a multilevel interconnect structure formed by stacking, a plural number of electrical circuits, an interlayer dielectric layer has also been provided, for example, between the interconnections in an upper level and the interconnections in the underlying level.
The use of ceramic-like silica thin films as a protective or insulating layer for electronic devices is known. For example, U.S. Pat. No. 4,756,977 teaches a method for coating electronic devices with a silica thin film in which a solvent solution of hydrogen silsesquioxane resin is coated on a substrate, the solvent is then evaporated, and heating to 150.degree. C. to 1,000.degree. C. is carried out in order to effect conversion into ceramic-like silica.
However, hydrogen silsesquioxane resins typically contain a considerable amount of volatile component. As a consequence, exposure to the high temperatures specified above can cause such problems as a diminution in film thickness and the generation of internal stresses in the film. Moreover, outmigration and expulsion of the volatile component can cause contamination of surrounding equipment.
Methods for removing the low-molecular-weight component in hydrogen silsesquioxane resin have been proposed. For example, U.S. Pat. No. 5,416,190 teaches removal of the low-molecular-weight component through addition of solvent to already synthesized hydrogen silsesquioxane resin. Unfortunately, the removal of low-molecular-weight component by this method yields hydrogen silsesquioxane resin that has a poor performance as a planarizing coating when applied on substrates. In addition to the fact that high-molecular-weight hydrogen silsesquioxane resin itself performs poorly as a planarizing coating for substrates, high-molecular-weight hydrogen silsesquioxane resin has a high softening point (at least 180.degree. C.) and its use for substrate planarization therefore requires heating and melting at high temperatures (at least 200.degree. C.). High-molecular-weight hydrogen silsesquioxane resin also has a poor capacity to fill into the topographical irregularities on substrates for electronic devices having a multilayered structure and as a consequence may not be fully satisfactory in some applications.
It is therefore an object of this invention is to provide a silica thin film forming composition that upon application to substrate performs well as a planarizing coating for the substrate and that can be converted by exposure to high-energy radiation into silica thin film with an excellent electrical insulating performance.
It is also an object of this invention is a method for the formation of silica thin films.
It is also an object of this invention to provide semiconductor devices that contain an electrically insulating layer that exhibits an excellent capacity to coat and planarize the interconnect structures on the substrate.
It is also an object of this invention to provide a method for the fabrication of such semiconductor devices.